Hi Nick,

As far as I know, the publish operation for image transport are in a "if 
(numSubscriber() > 0) { ... publish ...} " block.
If there is no subscriber, the serialisation code should  not be  called 
at all, so the cost should be very close to 3.

On 12/06/10 17:19, Nicholas Butko wrote:
> Does anyone familiar with the details of roscpp or imae_transport know, specifically in the context of no subscribers, (a) how much overhead is there to publish something? and (b) does that overhead scale with the size of the message?
>
> Specifically I am interested in the case of images. Consider three cases:
>
> 1) a node publishes an image, and it is shown in image_view
> 2) a node publishes an image, but it is not shown in image_view or anywhere else
> 3) a node does not publish an image
>
> Clearly there will be a lot more computation associated with (1) than (3), but what about (2) -- is it closer to (1) or (3) or somewhere close to the middle?
>
> --Nick
> _______________________________________________
> ros-users mailing list
> ros-users@code.ros.org
> https://code.ros.org/mailman/listinfo/ros-users
>    

-- 
Dr. Cedric Pradalier
http://www.asl.ethz.ch/people/cedricp